Cleans up orphan compute_nodes not cleaned up by compute manager

Fixes bug 1161193

Orphan compute_node records can cause the scheduler to pick
compute nodes that are not handled by driver anymore. This
can happen if you rename your hypervisor_hostname or in a
multi-node support where driver does not support a node
anymore for whatever reason (hardare failure for example).

Also, removing resource tracker logic to delete nodes since
resource trackers built in compute manager will never accept
nodes not reported by driver

Change-Id: I742d2e81ec0592d952ee5736aa8dce1e5598ef80
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp